glusterd: Save/restore/sync rebalance dict

A dictionary was added to store additional information of a rebalance
process, like the bricks being removed in case of a rebalance started
by remove-brick. This dictionary wasn't being stored/restored or synced
during volume sync, leading to errors like a volume status command
failing. These issues have been fixed in this patch. The rebalance dict
is now stored/restored and also exported/imported during volume sync.

Also, this makes sure that the rebalance dict is only create on
remove-brick start. This adds a bricks decommissioned status to the
information imported/exported during volume sync.

Change-Id: I56fed23dc2de80a96648055fe705e9c3ffd55227
BUG: 1040809
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/6492
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>